UNIVERSITY   OF  CALIFORNIA  PUBLICATIONS 

COLLEGE  OF  AGRICULTURE 

AGRICULTURAL  EXPERIMENT  STATION 

BERKELEY,  CALIFORNIA 


IRRIGATION  OF  ALFALFA 
IN  IMPERIAL  VALLEY 


BY 

WALTER  E.  PACKARD 


BULLETIN  No.  284 

September,   1917 


UNIVERSITY  OF  CALIFORNIA  PRF.SS 

BERKELEY 

1917 


Benjamin  Ide  Wheeler,  President  of  the  University. 

EXPEEIMENT  STATION  STAFF 

HEADS    OF   DIVISIONS 

Thomas  Forsyth  Hunt,  Director. 

Edward  J.  Wickson,  Horticulture    (Emeritus). 

Herbert  J.  Webber,  Director  Citrus  Experiment  Station;   Plant  Breeding 

Hubert  E.  Van  Norman,  Vice-Director;  Dairy  Management. 

William   A.   Setchell,  Botany. 

Myer  E.  Jaffa,  Nutrition. 
*Eobert  H.  Loughridge,  Soil  Chemistry  and  Physics   (Emeritus). 

Charles  W.  Woodworth,  Entomology. 

Ealph  E.  Smith,  Plant  Pathology. 

J.  Eliot  Coit,  Citriculture. 

John  W.  Gilmore,  Agronomy. 

Charles  F.  Shaw,  Soil  Technology. 

John  W.  Gregg,  Landscape  Gardening  and  Floriculture. 

Frederic  T.  Bioletti,  Viticulture  and  Enology. 

Warren  T.  Clarke,  Agricultural  Extension. 

John  S.  Burd,  Agricultural  Chemistry. 

Charles  B.  Lipman,  Soil  Chemistry  and  Bacteriology. 

Clarence  M.  Haring,  Veterinary  Science  and  Bacteriology 

Ernest  B.  Babcock,  Genetics. 

Gordon  H.  True,  Animal  Husbandry. 

James  T.  Barrett,  Plant  Pathology. 

Fritz  W.  Woll,  Animal  Nutrition. 

Walter  Mulford,  Forestry. 

W.  P.  Kelley,  Agricultural  Chemistry. 

H.  J.  Quayle,  Entomology.  • 

Elwood  Mead,  Rural  Institutions. 

J.  B.  Davidson,  Agricultural  Engineering. 

H.  S.  Reed,  Plant  Physiology. 

D.  T.  Mason,  Forestry. 

C.  L.  Roadhouse,  Dairy  Industry, 
t  Frank  Adams,  Irrigation  Investigations. 

W.  L.  Howard,  Pomology. 

William  G.  Hummel,  Agricultural  Education. 

John  E.  Dougherty,  Poultry  Husbandry. 

S.  S.  Rogers,  Olericulture. 

David  N.  Morgan,  Assistant  to  the  Director. 

Mrs.  D.  L.  Bunnell,  Librarian. 

Division  of  Agronomy 
J.  W.  Gilmore  W.  E.  Packard 

P.  B.  Kennedy  R.  L.  Adams 

B.  A.  Madson  Geo.  W.  Hendry 

H.  H.  Yost 


*  Died  July  1,  1917. 

t  In  co-operation  with  office   of  Public  Roads  and  Rural  Engineering,   U.   S. 
Department  of  Agriculture. 


IRRIGATION  OF  ALFALFA  IN 
IMPERIAL  VALLEY 

By  WALTEK  E.  PACKAED 


ALFALFA  IRRIGATION1 

Recent  investigations  have  indicated  certain  desirable  changes  in 
the  methods  of  irrigating  alfalfa  in  Imperial  Valley,  which,  if  carried 
out  will  tend  to  increase  yields.  At  present  the  annual  yields  vary 
from  two  and  one-half  to  ten  tons  per  acre  (besides  winter  pasturage)  ; 
four  and  one-half  tons  being  a  fair  average  for  the  whole  valley.  The 
wide  variation  is  due  to  the  great  difference  in  the  character  of  the 
soils  and  to  the  fact  that  some  fields  are  irrigated  more  efficiently  than 
others.  Alkali  is  a  factor  in  the  low  productiveness  in  some  cases,  but 
taking  the  valley  as  a  whole,  "alkali"  is  not  the  main  cause  for  low 
yields.  Although  it  is  certain  that  the  "softer"  or  sandier  types  of 
soil  are  better  adapted  to  alfalfa  than  the  ' '  harder ' '  or  heavier  types, 
experiments  have  shown  that  careful  irrigation  will,  in  a  large  meas- 
ure, eliminate  the  differences  between  yields  obtained  on  these  types. 
The  number  of  cuttings  and  the  yields  secured  from  an  established 
stand  of  alfalfa  depend  almost  entirely  upon  the  efficiency  of  irri- 
gation. 

PEEPAEING  LAND  FOE  IEEIGATION 

A  field  which  is  to  be  planted  to  alfalfa  should  be  especially  well 
prepared.  Any  neglect  in  proper  leveling  will  often  cause  much 
trouble  and  some  loss  during  the  entire  time  that  the  crop  occupies 
the  land,  while  carelessness  in  forming  the  seed  bed  may  result  in  a 
thin  stand,  with  the  resultant  introduction  of  Bermuda  grass.  The 
actual  loss  in  crop  area  is  often  considerable  (from  5  to  15  per  cent) 
while  the  slow  growth  of  the  alfalfa  on  high  places  in  the  field  not 
receiving  sufficient  water,  represents  an  unnecessary  financial  loss 
to  the  farmer. 


1  Based  in  part  on  work  done  in  cooperation  with  the  Office  of  Public  Eoads 
and  Eural  Engineering,  U.  S.  Department  of  Agriculture  and  the  State  Depart- 
ment of  Engineering  of  California.  The  measurements  of  water  applied  to  alfalfa 
fields  and  the  field  studies  of  its  distribution  in  the  soil  and  in  part  the  examination 
of  water-logged  lands  were  made  by  F.  J.  Veihmeyer,  Assistant  Irrigation  Engi- 
neer, Office  of  Public  Eoads  and  Eural  Engineering. 


68  UNIVERSITY  OF  CALIFORNIA EXPERIMENT  STATION 

Land  which  has  never  been  plowed  should  be  turned  to  a  depth  of 
from  four  to  six  inches,  while  land  which  has  been  plowed  will  be 
benefited  by  a  deeper  working.  If  the  land  is  moist,  discing  should 
follow  the  plowing  each  day  in  order  to  prevent  the  ground  surface 
from  becoming  too  lumpy.  The  borders  should  be  rebuilt  and 
straightened.  A  thorough  irrigation  will  indicate  any  irregularities 
in  the  surface  which  may  have  been  overlooked.  After  the  land  is 
well  leveled  and  irrigated,  discing  and  harrowing  will  prepare  the 
surface  for  seeding. 

Seeding. — Alfalfa  can  be  satisfactorily  broadcasted  or  seeded  with 
a  drill.  Experiments  have  so  far  indicated  that  drilling  is  the  prefer- 
able practice,  if  the  seed  is  not  planted  too  deeply  (not  deeper  than 
one-half  inch  in  heavy  soils,  or  one  and  one-half  inches  in  light  soil). 
Some  remove  the  seed  tubes  from  behind  the  drill  discs  in  order  to  pre- 
vent this  deep  seeding,  especially  where  the  land  is  to  be  irrigated 
immediately  after  planting. 

October  is  considered  the  best  month  for  planting,  although  alfalfa 
can  be  successfully  sown  at  almost  any  time  between  October  1  and 
April  15.  The  heavy  content  of  silt  in  the  irrigation  water  during 
periods  in  the  fall  is  the  greatest  objection  to  fall  planting,  while  the 
heavy  winds  often  cause  much  trouble  in  the  spring. 

Irrigation  at  the  Time  of  Seeding. — Irrigation  of  the  young  alfalfa 
is  a  particular  operation.  The  soil  should  be  well  wetted  by  a  thor- 
ough irrigation  before  planting.  Where  the  seed  is  drilled  in  and 
not  irrigated,  the  fields  should  be  "planked"  or  dragged  in  order  to 
compact  the  earth  about  the  seed  to  insure  germination.  No  irrigation 
should  be  given  until  the  plants  develop  from  three  to  four  true 
leaves.  Where  the  seed  is  irrigated,  which  is  the  custom  in  Imperial 
Valley,  the  first  irrigation  after  planting  should  be  followed  by  a 
second  light  irrigation  in  from  three  to  five  days.  The  silt  carried  by 
the  irrigation  water  often  forms  an  almost  impenetrable  crust  soon 
after  irrigation  and  with  the  harder  types  of  soil  the  surface  itself 
becomes  so  hard  and  dry  for  a  quarter  of  an  inch  or  more  that  the 
young  plants  cannot  come  through.  The  second  irrigation  recom- 
mended tends  to  overcome  this  hardening  and  drying  and  usually 
insures  a  good  stand.  It  is  important,  however,  that  this  second  irri- 
gation should  come  before  the  plants  appear  above  the  ground,  on 
account  of  the  fact  that  irrigation  of  the  young  plants  with  muddy 
water  before  the  third  or  fourth  true  leaf  appears  will  usually  injure 
the  seedlings,  in  many  cases  killing  so  large  a  percentage  as  to  seri- 
ously deplete  the  stand.  Withholding  the  water  from  the  young 
plants  after  they  are  well  sprouted  will  ordinarily  not  cause  a  loss, 


IRRIGATION  OF  ALFALFA  IN  THE  IMPERIAL  VALLEY 


69 


for  though  the  surface  crust  may  appear  very  dry,  the  roots,  which 
attain  a  penetration  of  from  eight  to  fifteen  inches,  as  shown  in  figure 
1,  within  three  weeks  after  seeding,  will  ordinarily  carry  the  plants 
through.  After  the  young  plants  have  developed  three  or  four  true 
leaves,  irrigation  may  proceed  in  the  usual  way. 


Fig.  1. — 1-2,  Alfalfa  Seedlings,  first  appearance  above  ground.  Too  young 
to  irrigate.  3-4,  Alfalfa  seedlings  too  young  to  irrigate  safely  with  silty  water, 
particularly  on  heavy  soils.  5-6,  Alfalfa  seedlings  large  enough  to  be  safe  from 
damage  from  silty  water  under  ordinary  conditions. 


WATEE  EEQUIEED  FOE  ALFALFA 

Alfalfa  requires  from  350  to  1000  tons  of  water  to  produce  one 
ton  of  cured  hay.2  The  wide  variation  in  water  requirement  is  due 
to  the  varying  condition  of  humidity  and  temperature  under  which 


2  The  Soil,  by  King,  the  MacMillan  Co. ;  Principles  of  Irrigation  Practice,  by 
Widsoe,  MacMillan  Co. ;  The  Water  Requirement  of  Plants,  by  Briggs  and  Shantz, 


70  UNIVERSITY  OF  CALIFORNIA EXPERIMENT  STATION 

the  plant  is  grown.  The  fact  that  alfalfa  grows  so  readily  in  the 
spring  and  fall  with  half  the  number  of  irrigations  required  in  the 
hot  and  dry  summer  months,  illustrates  that  fact.3  In  this  section 
where  the  temperatures  are  so  high  and  the  humidity  so  low,  tran- 
spiration is  probably  greater  than  in  most  alfalfa-growing  sections 
of  this  country,4  and  an  unusually  large  amount  of  water  is  required. 
As  this  report  is  not  a  study  of  the  duty  of  water  for  alfalfa  the 
question  of  the  amounts  used  will  not  be  discussed. 

Wilting  Point — Amount   of   Water   Necessary  for   Plant   Growth 

Not  only  does  alfalfa  require  a  large  amount  of  water  but  the 
water  must  be  applied  in  the  right  quantities  in  order  that  the  plant 
may  utilize  it.  It  is  impossible  for  any  plant  to  remove  all  of  the 
water  from  a  soil  on  account  of  the  adhesion  of  the  water  to  the  small 
soil  particles.  The  fact  that  damp  sand  holds  together  while  dry  sand 
or  sand  held  under  water  does  not,  illustrates  this  drawing  power. 

This  wilting  point  varies  in  different  soils  from  2  per  cent  of 
moisure  present  in  the  coarse  sands  to  18  per  cent  in  the  finest  clay. 
As  the  soil  on  any  farm  is  a  combination  of  distinct  types,  usually 
occurring  in  layers  of  various  thicknesses,  although  sometimes  being 
a  more  or  less  homogeneous  mixture,  the  wilting  coefficient  of  the 
average  soil  in  the  field  is  usually  some  combination  of  the  figures 
given,  as  indicated  by  the  table  accompanying  the  soil  charts,  which 
give  the  wilting  coefficient  of  the  various  types  of  soil  found  in  the 
fields  studied.  When  it  is  realized,  however,  that  alfalfa  planted  on 
the  sandiest  types  of  soil  in  the  valley  would  not  wilt  until  the  moist- 
ure reaches  the  low  limit  of  2  or  3  per  cent,  while  alfalfa  planted  in  a 
plat  of  heavy  clay  soil  would  wilt  when  18  per  cent  of  moisture  is 
present,  it  can  be  seen  that  the  soils  found  here  must  receive  different 
treatment  in  order  to  get  similar  results. 

Saturation  of  the  Soil  not  Desirable 

Too  much  water  is  as  undesirable  as  too  little,  for  plants  need  air 
as  well  as  moisture.  Too  much  water  usually  causes  the  greater  losses, 
for  it  necessitates  drainage  in  many  cases  in  addition  to  the  loss  of 
the  crop.      Although  it  is  impossible  to  say  just  what  percentage  of 

3  Although  the  greater  transpiration  during  the  summer  is  probably  the  main 
cause  for  reduced  growth  during  that  period,  the  effect  of  the  intense  sunlight 
undoubtedly  has  a  detrimental  effect  on  the  summer  growth  of  the  alfalfa,  as 
pointed  out  by  William  Lawrence  Balls  in  his  book  entitled  The  Cotton  Plant  in 
Egypt — Studies  in  Physiology  and  Genetics,  MacMillan  Co.,  London,  1912. 

4  No  measurements  have  been  made  of  the  transpiration  in  this  section,  but 
from  conclusions  made  by  Briggs  and  Shantz  in  Plant  Ind.  Bull.  284,  U.  S.  D.  A., 
it  can  be  assumed  that  transpiration  is  very  great  in  this  section. 


IRRIGATION  OF  ALFALFA  IN  THE  IMPERIAL  VALLEY 


71 


moisture  is  needed  to  maintain  a  maximum  growth  of  alfalfa,  it  is 
safe  to  conclude  that  the  moisture  content  in  the  soil  must  be  some- 
where above  the  wilting  point  and  below  saturation. 

Conditions  Suitable  for  Control  of  Moisture 

As  the  rainfall  in  this  section  averages  below  four  inches  per  year, 
the  valley  soils  are  dust-dry  to  a  considerable  depth  before  irrigation 
water  is  added.  The  moisture  found  in  the  surface  soil  must,  there- 
fore, come  either  from  seepage  from  canals  or  from  direct  irrigation. 
This  allows  an  almost  perfect  control  of  soil  moisture  by  the  irrigator 


Fig.   2. — Separating  alfalfa  roots  from  soil  by  hand.      Roots   are  later   washed, 

dried  and  weighed. 

and  at  the   same  time  affords   excellent  conditions   under  which   to 
study  the  problems  of  moisture  penetration. 


GENERAL  SURVEY  OF  EXISTING  CONDITIONS 

A  general  survey  of  the  moisture  condition  in  the  valley  soils 
showed  a  wide  variation  in  depth  of  penetration,  as  might  naturally 
be  expected.  In  the  hard  and  medium  hard  soils  the  penetration 
averaged  about  three  feet,  while  in  many  cases  water  had  not  pene- 
trated for  more  than  two  feet  after  two  or  three  years  of  irrigation. 
In  the  medium  soft  soils  the  condition  is  usually  good,  the  moisture 
penetrating  to  a  depth  of  from  ten  to  fifteen  feet,  with  no  excess 
accumulation  in  the  lower  strata.  The  sandy  soils  are  commonly 
over-irrigated.      In  many  places  with  sandy  soils  water  stands  from 


72 


UNIVERSITY  OF  CALIFORNIA EXPERIMENT  STATION 


two  to  ten  feet  from  the  ground  surface,  especially  where  the  porous 
sand  overlies  impervious  clay. 

Eoot  Development 

In  connection  with  this  investigation  a  study  was  made  of  root 
development  in  different  types  of  soil  and  under  varying  water  con- 
ditions in  order  to  know  how  the  feeding  roots  responded  to  irrigation. 
An  area  three  feet  square  was  selected  in  an  average  location  on  each 
field  studied  and  the  soil  removed  to  the  full  depth  of  root  penetration, 
agitated  until  all  soil  particles  were  washed  away,  leaving  a  mass  of 


Fig. 


3. — Separating  soil   from  roots  by  placing   soil   mass  in   a   screen  box   and 
agitating  in  an  irrigation  ditch. 


roots.  The  roots  of  various  sizes  were  sorted  out  and  the  smallest 
with  a  diameter  of  1  mm.  or  less  were  rewashed,  air-dried,  and 
weighed.  Charts  were  made  representing  the  distribution  of  these 
roots  in  each  foot  to  the  full  depth  of  root  penetration.  It  is  assumed 
a  six-inch  layer  being  removed  at  a  time.  The  soil  was  placed  in  a 
screen  box  and  the  whole  held  under  water  in  an  irrigation  ditch  and 
that  these  small  roots  represent  the  feeding  roots  of  the  alfalfa  and 
that  the  charts  representing  the  distribution  of  these  feeding  roots 
really  represent  graphically  the  feeding  zone  of  the  alfalfa  plant. 


A  Large  Proportion  of  Feeding  Eoots  are  in  the  Surface  Soil 

The  most  striking  feature  brought  out  by  the  charts  is  that  from 
80  to  90  per  cent  of  the  fine  roots  are  found  in  the  upper  four  feet 


IRRIGATION  OF  ALFALFA  IN  THE  IMPERIAL  VALLEY 


73 


CHART    NO.  1 


z*2 


t-  U  X 


DISTRIBUTION  OF  FEEDING  ROOTS  OF 
ALFALFA  IN  FINE  SANDY  LOAM  SOIL  IN 
IMPERIAL  VALLEY.  NO  WATER  TABLE  WITHIN 
15  FT.  OF  GROUND  SURFACE. 


DISTRIBUTION  OF  FEEDING  ROOTS  OF 
ALFALFA  IN  SANDY  LOAM  SOIL  AT  EL  MONTE 
CAL.  WATER  TABLE  VARYING  FROM  4  TO  9 
FEET  BELOW  THE  GROUND  SURFACE. 


51 

03 


O: 


74  UNIVERSITY  OF  CALIFORNIA EXPERIMENT  STATION 

where  the  land  receives  frequent  surface  irrigations.  Deep  roots  can 
be  formed  by  a  system  of  deep  irrigation,  as  described  in  chart  No.  3 
but  under  ordinary  conditions  the  largest  mass  of  feeding  roots  is 
developed  in  the  top  zone.  Alfalfa  has  always  been  represented  as  a 
deep-rooted  crop,  which  it  is,  but  it  is  very  apparent  that,  under 
the  conditions  represented  by  these  charts,  a  very  small  percentage 
of  the  roots  go  below  five  feet.  In  the  type  of  soil  and  under  the 
conditions  described  a  majority  of  the  small  roots  are  in  the  upper 
two  feet,  which  fact  indicates  that  it  is  very  essential  to  give  this 
upper  zone  particular  attention  in  any  system  of  irrigation  designed 
to  secure  large  yields. 


Need  of  Organic  Matter  Demonstrated 

The  presence  of  organic  matter  has  a  very  noticeable  effect  on  the 
development  of  the  feeding  roots,  as  indicated  by  the  fact  that  when- 
ever a  stratum  containing  much  organic  matter  is  encountered  the 
feeding  roots  are  always  very  numerous.  A  perfect  network  of  these 
fine  roots  gathers  about  a  piece  of  decaying  wood  or  follows  down  the 
channels  left  by  roots  of  native  vegetation  which  formerly  occupied 
the  land.  The  larger  roots  often  pass  through  a  sandy  stratum  con- 
taining little  organic  matter  without  sending  out  very  many  fine 
roots  until  the  heavier,  richer  soil  is  reached. 

This  is  well  illustrated  in  chart  No.  2.  The  fine  roots  were  very 
much  more  numerous  in  this  location  than  in  any  Imperial  Valley 
soils  studied.  The  only  reasonable  explanation  of  this  fact  is  that 
the  comparatively  large  amount  of  organic  matter  found  in  the  El 
Monte  soils  induced  this  greater  root  development  and  in  part 
accounts  for  the  large  yields  secured  on  these  non-irrigated  lands.5 
The  number  of  fine  roots  in  the  different  soil  strata  varies  with  the 
amount  of  organic  matter  present,  which  accounts  for  the  fact  that 
in  the  chart  more  roots  are  indicated  in  the  third  than  in  the  second 
foot  and  more  in  the  fifth  than  in  the  fourth. 

It  is  very  evident  that  the  soils  of  Imperial  Valley  need  more 
organic  matter,  and  anything  that  can  be  obtained  to  supply  this 
need  should  be  added  whenever  possible. 

The  charts  represent  so  many  varied  conditions  that  each  will 
be  discussed  separately. 


s  The  very  large  percentage  of  roots  in  the  surface  stratum,  as  indicated  by 
the  chart,  is  probably  too  great  on  account  of  the  fact  that  it  was  impossible 
to  separate  out  all  of  the  organic  material  other  than  roots.  This  may  have 
had  an  effect  on  the  total  quantity  in  these  soils. 


IRRIGATION  OF  ALFALFA  IN  THE  IMPERIAL  VALLEY 


75 


CHART    No.  3 


S5 

oo 


DISTRIBUTION  OF  FEEDING  ROOTS  OF 
ALFALFA  IN  SANDY  LOAM  SOIL  IN  IMPERIAL 
VALLEY.  SATURATION  AT  15  FEET.  INFRE- 
QUENT BUT  HEAVY  IRRIGATION. 


76  UNIVERSITY  OF   CALIFORNIA — EXPERIMENT  STATION 


DISCUSSION  OF  CONDITIONS  REPRESENTED  BY  THE  CHARTS 

Chart  No.  1  represents  the  weights  of  feeding  roots  in  each  foot 
in  depth  in  the  field  giving  the  highest  yield  of  alfalfa  of  those  studied. 
The  alfalfa  was  nine  years  old  and  produced  from  six  to  nine  tons 
per  acre  besides  winter  pasture,  in  an  average  of  six  cuttings.  The 
soil  is  a  sandy  loam  to  a  depth  of  five  or  six  feet  and  from  there 
to  twelve  feet,  clay,  clay  loam,  and  sandy  loam  strata  alternate.  The 
greatest  number  of  roots  is  in  the  second  foot,  with  95  per  cent  in  the 
upper  four  feet,  which  is  to  be  expected  in  a  soil  where  all  of  the 
moisture  is  supplied  on  the  surface  by  irrigation  and  none  by  sub- 
irrigation. 

The  moisture  in  this  field  had  penetrated  to  a  depth  of  more  than 
fifteen  feet.  No  water  table  existed  at  this  depth,  although  the  lower 
strata  were  very  near  the  saturation  point.  Water  was  applied  at 
more  frequent  intervals  than  on  any  of  the  fields  under  observation, 
so  that  the  top  foot  of  soil  seldom  dried  out  to  below  the  wilting 
point,  during  the  period  between  irrigations.  The  value  of  this  sys- 
tem of  frequent  light  irrigations  is  at  once  apparent  for  the  roots  in 
this  field  go  to  a  depth  of  eleven  feet,  and  in  all  of  that  area  the 
percent  of  moisture  in  the  soil  between  irrigations  ranges  between 
saturation  and  the  wilting  point,  always  affording  ample  moisture  for 
all  roots. 

It  seems  apparent  therefore  that  frequent  irrigation,  sufficiently 
light  to  prevent  a  water-logging  of  the  soil  and  at  the  same  time 
sufficient  to  allow  for  deep  penetration  will  keep  up  the  moisture 
supply  in  the  zone  of  greatest  root  development  and  will  as  a  result 
give  the  largest  yields.  One  heavy  irrigation  may  add  as  much 
water  as  two  light  irrigations,  but  in  the  one  case  much  of  the  water 
will  be  lost  by  seeping  below  the  root  zone,  while  in  the  others  the 
water  will  be  largely  retained  in  the  top  soil  as  available  moisture  for 
plant  growth. 

Chart  No.  3  represents  the  deepest-rooted  alfalfa  studied.  The 
soil  is  a  sandy  loam  for  a  depth  of  six  feet  where  a  five  to  six-foot 
stratum  of  clay  loam  and  clay  begins.  The  field  produces  from  five  to 
six  tons  of  alfalfa  hay  per  year  besides  winter  pasture.  When  this 
land  was  leveled  a  large  amount  of  water  was  used  which  undoubtedly 
saturated  the  lower  soil  strata.  After  the  alfalfa  stand  was  about  a 
year  old  the  ranch  was  sold  and  no  water  was  applied  to  this  field  for 
about  ten  months.  During  this  time  the  alfalfa  roots  depended  upon 
the  moisture  already  in  the  soil  to  maintain  plant  growth,  and  as  a 
result  the  feeding  roots  were  developed  in  the  full  depth  of  twelve 


IRRIGATION  OF  ALFALFA  IN  THE  IMPERIAL  VALLEY 


77 


CHART    NO.  4 


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DISTRIBUTION  OF  FEEDING  ROOTS  OF 
ALFALFA  IN  SANDY  LOAM  SOIL  IN  IMPERIAL 
VALLEY.  WATER  TABLE  AT  4y2  FEET  BELOW 
THE  GROUND  SURFACE. 


WEIGHT  OF  ROOTS  IN  GRAMS 


CHART    NO.  5 
DISTRIBUTION    OF    FEEDING    ROOTS    OF 
ALFALFA  IN  SANDY  SOIL  IN  IMPERIAL  VALLEY 
WITH    WATER    TABLE    3    FEET    BELOW    THE 
GROUND  SURFACE. 


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6.5 


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6.5 


H.1 


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SANDY      LOAM 


SAND 


W.1 


CLAY         LOAM 


CLAY 


FINE  SANDY 
LOAM 


78  UNIVERSITY  OF  CALIFORNIA EXPERIMENT  STATION 

feet.6  During  this  period  the  alfalfa  did  not  grow  fast,  as  a  majority 
of  the  feeding  roots  of  the  plant  were  located  in  the  top  soil  where 
there  was  not  sufficient  moisture  for  plant  growth,  the  plant  maintain- 
ing itself  through  the  roots  in  the  moist  strata  below. 

The  condition  just  described  is  often  found  in  sections  where  no 
irrigation  water  is  applied  to  the  field,  but  where  the  roots  go  down 
to  water,  as  shown  in  chart  No.  2.  This  represents  the  distribution  of 
roots  in  a  sandy  soil  near  the  San  Gabriel  River  at  El  Monte,  Los 
Angeles  County,  where  the  alfalfa  is  not  irrigated.  The  El  Monte 
field  was  selected  to  illustrate  this,  as  no  alfalfa  is  grown  without  irri- 
gation in  Imperial  Valley.  In  this  field  the  water  table  varies  from 
four  feet  to  nine  or  ten  feet  below  the  surface  of  the  ground.  In  the 
winter,  during  the  rainy  period  when  the  San  Gabriel  River  is  high, 
the  water  stands  at  the  highest  point. 

The  alfalfa  makes  the  most  rapid  growth  in  the  spring,  as  the 
rain  keeps  the  moisture  well  above  the  wilting  point  at  the  ground 
surface  and  the  water  table  at  four  feet  furnishes,  by  capillarity, 
sufficient  moisture  for  maximum  plant  growth  in  the  top  root  zone. 
When  the  rains  stop  and  the  water  table  lowers,  the  growth  slackens 
up  and  during  the  dry  weather  when  the  top  soil  is  relatively  dry  the 
alfalfa  does  not  much  more  than  maintain  itself.  The  fine  roots  which 
tend  to  follow  the  water  down  keep  about  even  with  the  water  plane 
and  thus  secure  enough  moisture  to  keep  the  plant  alive  and  to 
support  some  growth  during  the  summer  months.  In  this  field  the 
roots  were  found  to  a  depth  of  eight  feet  while  water  was  encountered 
at  nine. 

Effect  of  Water  Table  on  Root  Development 

Much  has  been  written  regarding  the  dangers  of  a  rise  of  water 
table,  as  large  areas  of  good  land  have  been  rendered  worthless  on  that 
account,  but  it  seems  evident  from  this  chart  and  others  that  follow, 
that,  where  alkali  is  not  a  factor,  no  apparent  damage  is  done  until 
the  water  table  rises  above  the  four-foot  mark  or  thereabouts.  The 
roots  are  rotted  off  wherever  they  are  submerged  for  any  length  of 
time,7  and  as  soon  as  the  water  table  rises  about  four  feet,  a  sufficient 
number  of  the  roots  are  killed  to  affect  the  plant.    If  water  rises  closer 

6  When  the  root  studies  were  made  the  land  was  dry  below  eight  feet  on 
account  of  the  fact  that  recent  irrigations  have  not  been  sufficient  to  penetrate 
for  more  than  eight  feet.  These  lower  roots,  although  not  dead,  were  of  no 
value  to  the  plant  as  they  were  in  dry  soil.  It  is  apparent,  therefore,  that  the 
roots  below  eight  feet  were  developed  during  the  ten  months  when  the  sub- 
stratum was  saturated  and  no  water  was  applied  to  the  surface  of  the  field. 

7  The  period  of  submergence  necessary  to  kill  the  roots  is  not  known,  except 
that  submergence  for  a  few  days  will  not,  but  for  two  or  three  months  will. 


IRRIGATION  OF  ALFALFA  IN  THE  IMPERIAL  VALLEY 


79 


than  three  feet  so  large  a  proportion  of  roots  are  affected  as  to  greatly 
reduce  the  yield  by  killing  all  but  the  more  resistant  plants.  In  the 
field  just  described  the  roots  below  four  feet  were  all  of  this  year's 
growth,  as  indicated  by  the  fact  that  they  branched  from  roots  which 
were  rotted  off  at  the  four-foot  level.      The  lower  strata  were  full  of 


Fig.  4. — Alfalfa  root  rotted  off  by  rise  of  water  table.     Two  small  roots  are  shown 
growing  from  the  main  root  after  water  table  had  lowered. 


fine  roots  of  previous  years'  growth  which  had  died  out  with  the  rise 
of  the  water  table. 

The  fact  that  the  rise  of  the  water  table  is  not  necessarily  injurious 
until  it  begins  to  reach  an  area  of  large  root  development  near  the  sur- 
face is  indicated  in  charts  No.  4  and  No.  5.  The  alfalfa  in  the  field 
represented  by  chart  No.  4  is  growing  above  a  water  table  varying 
from  four  to  six  feet.      As  a  result  all  of  the  feeding  roots  are  in 


80  UNIVERSITY  OF  CALIFORNIA EXPERIMENT  STATION 

the  top  four  feet,  the  greatest  number  being  in  the  top  foot.  This 
field  is  being  damaged  by  the  existence  of  a  high  water  table,  but  is 
still  producing  good  crops.  The  geld  is  flooded  very  heavily  and 
water  often  stands  on  the  alfalfa  several  hours  before  it  finally  dis- 
appears. The  roots  which  had  penetrated  below  four  feet  before 
the  rise  of  water  table  were  decayed,  but  the  effect  was  not  serious 
enough  to  kill  the  plants  on  accoount  of  the  fact  that  a  sufficient 
quantity  of  roots  existed  in  the  upper  four  feet  to  maintain  a  normal 
growth. 

....  - ._ 


Fig.  5. — Bermuda  grass  soon  occupies  the  land  when  alfalfa  has  been  killed  out 
by  excessive  flooding  or  by  rise  of  water  table. 

In  the  field  represented  by  chart  No.  5,  however,  the  alfalfa  is 
rapidly  dying  out  and  Bermuda  grass  taking  its  place.  The  water 
table  in  this  case  is  so  close  to  the  surface  that  a  large  majority  of 
the  roots  are  killed,  leaving  only  the  top  two  feet  as  a  feeding  zone. 

It  seems  apparent,  therefore,  that,  so  far  as  the  water  table  is  con- 
cerned, alfalfa  will  produce  large  yields  if  the  water  does  not  come 
close  enough  to  the  surface  to  rot  a  large  percentage  of  the  roots.  The 
frequent  testimony,  both  from  this  section  and  others,  that  alfalfa 
does  better  with  a  water  table  at  four  feet  than  when  no  water  table 
exists  is  probably  based  on  the  fact  that  a  water  table  at  that  depth 
tends  to  maintain  a  maximum  moisture  condition  in  the  top  soil  by 


IRRIGATION  OF  ALFALFA  IN  THE  IMPERIAL  VALLEY  81 

capillarity.  If  the  water  table  is  within  three  feet  of  the  surface  and 
remains  constant,  alfalfa  will  often  produce  good  crops,  as  it  does  in 
part  of  the  San  Joaquin  Valley  where  this  condition  exists,  but  when 
the  water  table  fluctuates  and  sometimes  rises  above  three  feet,  so 
large  a  number  of  roots  are  rotted  as  to  greatly  reduce,  if  not  entirely 
kill  out  the  stand.  When  alkali  is  present  in  sufficient  quantities  in 
water-logged  lands,  the  salts  tend  to  concentrate  on  the  surface  and 
often  become  so  strong  as  to  kill  all  vegetation. 

Eoot  Development  and  Moisture  Distribution   in   Clays   and   Clay  Loams 

In  so-called  "hard  soils"  the  feeding  roots  are  necessarily  largely 
on  the  surface,  as  the  irrigation  water  often  does  not  penetrate  for 
more  than  three  to  four  feet.  If  a  large  yield  of  alfalfa  is  secured 
on  this  type  of  soil  it  is  necessary  to  keep  the  moisture  content  of 
the  top  soil  above  the  wilting  point  by  frequent  irrigations.  It  is 
apparent  that  if  by  infrequent  irrigation  the  top  foot  or  two  dry  out, 
the  roots  in  that  zone  are  of  no  use  to  the  plant  until  further  irrigation 
brings  the  water  in  the  soil  above  the  wilting  point.  This  condition 
is  very  common  in  the  valley  and  usually  accounts  for  the  fact  that 
alfalfa  grows  slowly  and  often  blossoms  when  only  a  foot  or  so  high 
on  the  harder  types  of  soil.  Frequent  irrigation  will  add  the  needed 
moisture  to  this  top  soil  area,  will  maintain  the  moisture  above  the 
wilting  point,  and  will  allow  for  a  rapid  growth  of  alfalfa. 

GENERAL  CONCLUSION 

In  order,  then,  to  get  satisfactory  yields  of  alfalfa  a  large  amount 
of  water  must  be  supplied  during  the  season,  it  must  be  supplied 
frequently  enough  so  as  to  prevent  a  drying  of  the  surface  soil  on 
the  one  hand  and  water-logging  of  the  soil  on  the  other.  This  desir- 
able condition  can  only  be  accomplished  by  conforming  the  grade 
of  the  land,  the  frequency  of  irrigation,  the  size  of  the  field,  and  the 
head  of  water  used  to  the  types  of  soil  to  be  handled.  As  the  soil 
types  vary  widely,  it  will  be  necessary  to  consider  each  general  type 
separately.  It  will  be  sufficient  for  this  purpose  to  divide  the  soils  of 
the  valley  into  three  general  classes,  sandy  or  porous  soils,  sandy  loams 
or  medium  soft  soils,  and  clay  loam  and  clay  or  heavy  soils. 

METHOD  OF  IRRIGATION  RECOMMENDED  FOR  POROUS  SOILS 

The  great  danger  in  all  sandy  or  porous  soils  is  that  too  much 
water  will  be  applied  and  a  high  water  table  thus  formed.  This  con- 
dition is  already  prevalent  in  some  sections,  where  sand  overlays  clay. 


82  UNIVERSITY  OF  CALIFORNIA EXPERIMENT  STATION 

The  clay  tends  to  retard  the  downward  movement  of  the  water,  and 
as  a  result  there  is  an  accnmnlation  of  water  above  this  stratum, 
which  gradually  rises  toward  the  surface  as  irrigation  continues.  This 
rise  of  water  table  can  be  prevented  in  a  majority  of  cases  by  adopting 
one  or  all  of  the  following  suggestions. 

Use  smaller  lands.  The  lands  or  borders  for  irrigation  on  this  type 
of  soil  should  usually  not  exceed  one-eighth  of  a  mile  in  length  and, 
if  necessary,  not  more  than  twenty-five  to  thirty  feet  in  width  in  order 
that  the  water  applied  may  reach  the  lower  end  without  oversaturat- 
ing  the  upper  end.  There  are  many  fields  in  the  valley  where  water 
has  been  run  from  a  quarter  to  a  half  mile  on  these  types  of  soil^  with 
the  inevitable  effect  of  adding  too  much  water  at  the  upper  portion 
of  the  field,  which  of  course  results  in  a  rise  of  water  table.  The 
exact  length  and  width  of  the  lands  must  depend  on  the  condition  of 
the  surface  and  the  degree  of  porosity  of  the  soil.  If  the  soil  is  very 
sandy  the  lands  should  be  both  narrow  and  short  in  order  to  allow  a 
quick  irrigation. 

Use  large  head.  In  addition  to  using  smaller- lands  than  are  now 
being  used,  it  would  be  an  advantage  in  nearly  all  cases  to  use  much 
larger  heads  of  water  than  are  at  present  used  on  this  type  of  soil. 
In  other  parts  of  California  a  head  of  from  eight  to  twelve  feet  is 
often  run  onto  one  land  in  order  to  get  quick  irrigation.  A  small 
head  will  often  disappear  so  rapidly  at  the  upper  end  that  it  takes  a 
very  long  time  to  cover  the  field.  The  size  of  head  must  conform  to 
the  size  of  the  land  and  the  character  of  the  soil,  the  point  being  to 
run  the  water  so  quickly  over  the  land  that  an  excess  above  the 
requirements  of  the  plants  will  not  be  added  to  any  part  of  it.  A 
head  of  three  to  eight  cubic  feet  per  second  for  the  very  sandy  soil 
and  from  two  to  four  cubic  feet  per  second  for  the  more  compact 
sandy  loams  would  not  be  too  great.  A  soil  auger  can  be  very  effect- 
ively used  in  determining  the  soil  moisture  condition  where  one  is 
uncertain  regarding  the  moisture  penetration. 

In  cases  where  the  grade  is  less  than  five  feet  to  the  mile  in  the 
directions  in  which  the  lands  are  built,  and  it  can  be  increased  to  a 
eight  to  ten  feet  to  the  mile  by  changing  the  direction  of  the  lands,  it 
should  be  done.  There  will  be  no  danger  of  the  soil  washing  at  that 
grade  and  it  will  materially  help  in  getting  the  water  across  the  land 
quickly. 

It  is  very  important  that  the  recommendations  made  be  followed 
out  in  case  of  light  sandy  soils  for  there  is  always  danger  of  the 
formation  of  water  table  when  water  penetration  is  rapid.  The  depth 
of  the  soil  should  not  be  considered  as  a  safeguard,  as  it  only  takes 


IRRIGATION  OF  ALFALFA  IN  THE  IMPERIAL  VALLEY  83 

time  to  saturate  the  large  soil  reservoir.  In  1910  ground  water  was 
found  at  a  depth  of  fifteen  feet  in  a  field  planted  to  alfalfa.  In  two 
years  the  level  had  raised  to  nine  feet,  so  that  water  stood  within  six 
feet  of  the  surface,  and  water  is  now  so  close  to  it  that  alkali  is  being- 
brought  up  and  deposited  on  the  ground  surface  by  capillary  action. 
Every  man  owning  "soft"  land  should  investigate  the  condition  in 
his  field  and  conform  his  irrigation  practice  to  meet  .the  conditions 
present. 

Drainage  is  Often  Necessary  in  Sandy  Soils 

In  some  cases  a  water  table  is  formed  through  seepage  from  canals, 
particularly  when  canals  are  located  in  sandy  territory  on  a  sufficient 
grade  to  prevent  a  deposit  of  fine  silt  on  the  bottom  and  sides.  The 
rate  of  seepage  is  so  great  under  these  conditions  that  the  effect  of 
a  rise  or  fall  in  the  water  level  in  a  canal  can  often  be  noticed  a  dis- 
tance of  one-eighth  of  a  mile  from  the  canal  within  twenty-four 
hours.  This  condition  can  only  be  handled  by  drainage  or  by  lining 
the  ditches  causing  the  seepage.  In  most  cases  the  ditches  in  the 
valley  are  on  such  slight  grade  that  the  deposits  of  silt  prevent  rapid 
seepage. 

When  a  ranch  is  near  a  deep  drain,  or  one  of  the  river  channels, 
a  satisfactory  system  of  drainage  can  be  installed  to  remove  the  excess 
of  water  which  may  have  accumulated  by  either  seepage  or  over- 
irrigation.  In  many  cases  such  facilities  do  not  exist  and  the  drain- 
age question  is  a  community  problem  which  must  be  met  as  such. 

A  surface  drain  at  the  end  of  a  field  will  be  of  great  value  in 
preventing  a  scalding  of  the  alfalfa  by  standing  water,  although  such 
drains  do  not  affect  the  ground  water  condition.  There  is  sometimes 
a  danger  of  depending  too  much  upon  these  drains,  with  the  result 
that  the  lower  ends  of  the  fields  are  badly  flooded,  but  where  properly 
used  much  waste  can  be  prevented.  "Experience  has  taught  the 
necessity  of  considerable  depth.  This  should  never  be  less  than  six 
feet — and  eight  feet  would  be  a  better  minimum. '  '8  The  outlet  drains 
would  have  to  be  still  deeper. 

METHOD  OF  IEEIGATION  EECOMMENDED  FOR  MEDIUM  SOILS 

The  sandy  loam  soils  are  easily  irrigated,  although  too  much  or 
too  little  water  is  sometimes  applied  with  the  usual  results.  There 
is  no  good  excuse,  however,  for  not  having  a  good  moisture  condition 
in  these  medium  soft  "soils.      If  the  alfalfa  does  not  grow  as  rapidly 


s  "The  Drainage  of  Irrigated  Land,"  by  R.  A.   Hart.      Bulletin   190,  U.   S. 
Dept.  of  Agr. 


84  UNIVERSITY  OF  CALIFORNIA EXPERIMENT  STATION 

as  desired  an  investigation  shonld  be  made  of  the  moisture  condition 
in  the  soil  by  the  use  of  a  soil  augur  or  a  spade.  If  the  top  soil 
appears  too  dry  before  irrigation  it  would  perhaps  be  wise  to  give  the 
field  an  additional  light  irrigation  between  cuttings.  If  the  lower 
strata  are  saturated  the  recommendations  given  for  hard  or  clay  soils 
should  be  followed. 

METHODS  OF  IRRIGATION  RECOMMENDED  FOR  COMPACT   SOILS 

The  problem  on  the  hard  type  of  soils  is  to  get  the  water  deep  into 
the  soil  in  sufficient  quantities  to  maintain  rapid  growth. 

In  many  cases  the  fact  that  the  surface  has  been  irrigated  is  taken 
as  evidence  that  the  water  has  soaked  in,  while  in  reality  only  the  top 
six  inches  have  been  wetted.  It  is  very  common  to  find  dry  soil  at 
a  depth  of  two  and  one-half  to  three  feet  in  these  heavy  soils.  In 
order  to  get  proper  penetration  the  following  recommendations  should 
be  followed  out. 

Size  of  land.  Land  should  be  from  an  eighth  to  a  quarter  mile 
long,  very  seldom  running  one-half  mile,  as  is  now  a  common  practice. 
It  is  difficult  to  handle  water  property  on  long  lands,  as  a  flooding  of 
the  lower  end  can  seldom  be  avoided.  On  land  that  is  comparatively 
flat,  borders  fifty  to  one  hundred  feet  apart  are  satisfactory,  but  when 
the  land  is  at  all  steep,  lands  should  be  narrowed  down  to  twenty-five 
to  thirty  feet  wide  so  that  a  small  head  will  cover  the  surface  evenly. 

Head  of  water  to  use.  In  order  to  get  proper  penetration,  it  is 
necessary  to  run  a  comparatively  small  head  for  a  long  time.  Fields 
which  yielded  from  two  and  one-half  to  three  tons  per  acre  per  year 
have  been  made  to  double  the  yield  through  this  system  of  irrigation. 
A  small  head  of  water  requires  a  much  longer  time  to  travel  over  the 
field  than  a  larger  head  and  allows  of  a  better  penetration.  Land 
which  could  be  wetted  only  to  a  depth  of  three  feet  when  large  heads 
were  used  were  successfully  wetted  to  a  depth  of  five  and  six  feet 
by  the  use  of  smaller  heads.  The  effect  of  smaller  heads  running  for 
a  longer  time  is  more  noticeable  with  furrow  irrigation  than  with 
flooding,  but  the  effect  is  marked  in  both  cases. 

Grade  of  land.  The  grade  of  hard  land  should  not  be  over  five 
or  six  feet  to  the  mile.  A  grade  of  four  feet  is  satisfactory  if  the  land 
is  properly  leveled. 

Drains  should  be  made  at  the  lower  ends  whenever  practicable,  as 
scalding  is  very  common  on  this  type  of  soil.  The  drains  should  be 
large  enough  to  prevent  the  accumulation  of  water  at  the  lower  ends. 


